<?php
// define array
$cities = array(
  "United Kingdom" => "London", 
  "United States" => "Washington", 
  "France" => "Paris", 
  "India" => "Delhi"
);

// search array for key
$a =  array_key_exists('India', $cities);
var_dump($a);
$a =  array_search('Delhi', $cities);
var_dump($a);
$a =  in_array('Delhi', $cities);
var_dump($a);

?>